#include<iostream>
using namespace std;
const int N = 1e5 + 10;
int h[N], ne[N], e[N], index;
int d[N];
int q[N];
int n, m;

void add(int a, int b)
{
	e[index] = b;
	ne[index] = h[a];
	h[a] = index++;
}
int bfs()
{
	int hh = 0, tt = 0;
	q[0] = 1;
	memset(d, -1, sizeof(d));
	d[1] = 0;
	while (hh <= tt) {
		int t = q[hh++];
		for (int i = h[t]; i != -1; i = ne[i]) {
			int j = e[i];
			if (d[j] == -1) {
				d[j] = d[t] + 1;
				q[++tt] = j;
			}
		}
	}
	return d[n];

}

int main()
{
	cin >> n >> m;
	memset(h, -1, sizeof(h));
	for (int i = 0; i < m; i++) {
		int a, b;
		cin >> a >> b;
		add(a, b);
	}
	cout << bfs() << endl;
	return 0;
}